1. Field of the Invention
The present invention relates to an arrangement for inhibiting the operation of an integrated circuit chip. More specifically, the invention provides an arrangement for preventing an IC chip from being operated in a system having a clock rate that is greater than a predetermined frequency.
Even more specifically, the invention is directed to an arrangement for detecting the clock rate of a system in which the chip is operating and comparing it to an on chip generated reference frequency which defines that maximum frequency at which the chip is to be operated. If the system clock rate exceeds the reference frequency, operation of the chip is prevented.
2. Description of Related Art
Integrated circuit (IC) chips are designed to operate in specific environments under predetermined operating conditions. These conditions may include operating frequency (clock rate), supply voltage (V.sub.cc), ambient temperature (TA), AC and DC conditions, etc. The chip must be operated within the ranges specified for that chip to assure that it will properly operate. Some ICs, however, may operate at a frequency greater than that for which they were designed even though their accuracy may be less than intended.
Marketing constraints and special customer requirements for IC chips may dictate that IC chip manufactured for a high specification, for example a high clock rate, may be sold to a customer who intends to operate the chip at a lower specification than that for which it was designed. For example, a customer needing a 33 MHz. clock rate chip may be sold a 50 MHz. clock rate chip. In other words, a higher specification chip may be sold as a lower specification chip. Such a situation does not cause a problem. However, the reverse situation does cause a problem.
Some unscrupulous merchants may buy ICs having a low specification at a low price, and then represent it as being a higher specification chip and sell it for a higher price than that for which it should be sold. Such a merchant may actually alter a label on the chip or otherwise mark it to indicate a higher specification that should be indicated to obtain unfair profits. This can greatly damage the reputation of the chip manufacturer and cause considerable market disruptions.
This problem frequently occurs in the CPU (Central Processing Unit) IC market. For example, the operating frequency for the CPU of an IBM compatible personal computer is often 33 MHz. or 40 MHz. Some merchants may buy a 33 MHz. CPU at a low price, re-mark it as a 40 Mhz. or higher CPU and sell it at a higher price.
So far, there have been essentially three approaches taken to solve this problem:
(1) IC manufacturers sell their products only to credible wholesale dealers or customers. Unfortunately, this approach does not control sales downstream (the aftermarket). There may be a long chain of resellers, any one of whom may remark the chip and attempt to "upgrade" it.
2) Reduce the safe operating range of IC products. This approach in general degrades the overall chip market. There is demand among certain users for the most powerful, high specification chips available. Those chips must be distinguished from the lower specification chips on the market.
(3) Replace the conventional printed label on IC products by laser optical label that is harder to modify. This approach is also ineffective. Even though the label is harder to modify, it can still be modified. Furthermore, making extremely difficult to modify labels is quite expensive and raises the cost of the IC chips for everyone.